Could you have an iodine deficiency?

January 17, 2025

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Iodine deficiency in the UK is generally accepted as a health problem from the past, but recent research suggests this may not be the case – Why is it a problem now?

A 2016 research study undertaken in the Southwest of England tested the urinary iodine levels of 308 pregnant women in late pregnancy. 73% were found to have suboptimal iodine levels.
A 2015 research study from the South East involved testing the urinary iodine levels of 100 pregnant women at their first antenatal visit. 76% were found to have urinary levels of iodine lower than the WHO recommendation.

The UK is said to be number 7 out of the 10^th most iodine-deficient nations in the world. Despite this, it has been largely ignored by public health and politicians.

Why does iodine matter?

Iodine is an essential trace element the body needs throughout life to make the hormone thyroxine. This is a vital hormone that regulates the daily physiological and metabolic functions of the body.

Iodine deficiency has serious consequences, especially in pregnancy, for the developing fetal brain. Pregnant women need 50% more iodine than non-pregnant women. A low intake of iodine in pregnancy has been linked to significantly lower intelligence scores and reduced reading ability in the offspring. It is also linked to pregnancy loss, preeclampsia, and low birth weight. In severe cases, it can cause cretinism and stillbirth. Ideally, iodine levels should be in the normal range before conception.

Which foods contain iodine?

The foods that are the highest in iodine are fish, seafood and seaweed. Cow’s milk is also a good source, as it is enriched with iodine, because of the addition of iodine to animal feed. Poultry, eggs, bread, nuts, fruit, and vegetables contain small amounts of iodine. In the UK, iodine is not routinely added to salt, as it is in many European countries, because too much salt is a cause of high blood pressure.

Who is at risk of iodine deficiency?

Those most at risk of iodine deficiency are people who don’t eat fish or seafood, and/or avoid cow’s milk. Some plant milk is fortified with iodine, but most are not. It’s important to take note of the iodine content of the milk you are drinking to ensure you are not missing out on all-important iodine.

Vegetarians and vegans are at risk of iodine deficiency and are advised to take an iodine supplement. They should check with a health professional that this is the correct dose. Pregnant women are also at risk of iodine deficiency because their iodine requirements increase in pregnancy.

How would you know if you were deficient in iodine?

Many people with slightly low levels of iodine will be unaware and have no symptoms. However, eventually, iodine stores become depleted and iodine deficiency results in an underactive thyroid gland, due to low levels of thyroxine. This is called hypothyroidism.

The symptoms and signs of hypothyroidism can come on very insidiously meaning it can be a long time before it is diagnosed. Sometimes low thyroxine levels are discovered incidentally, on a blood test. At other times, your doctor may be alerted that you could be hypothyroid because of various symptoms and signs.

Weight gain:
- When thyroxine levels are low, your metabolic rate slows, and this is associated with weight gain. Massive weight gain is unusual. It is usually 5-10 pounds.
Feeling weak:
- Because your body is releasing energy less efficiently, you feel weak and tired.
Tiredness and fatigue:
- The tiredness associated with hypothyroidism is not the usual tiredness you experience after a bad night’s sleep. It’s a deep sense of fatigue that makes you feel exhausted and can interfere with your ability to function normally.
Dry skin and nails:
- Hypothyroidism results in under activity of the sweat glands. As a result, your skin becomes dry and flaky. You can also get dry, brittle nails, with vertical white ridges.
Hair loss:
- Hypothyroidism slows the rate of hair growth, plus disrupt the hair cycle. There may be generalised thinning of the hair and loss of eyebrows.
Feeling cold:
- When the levels of thyroxine are low, this slows the metabolic rate and can lower your core temperature. This means sufferers feel cold a lot of the time, even on a warm day.
A slow pulse:
- Low levels of thyroxine result in the heart beating more slowly. As it is also linked to raised cholesterol levels, there is an increase in arterial stiffness, and sometimes raised diastolic (lower reading) blood pressure.
Constipation:
- When thyroxine levels are low, this also slows gut motility, meaning intestinal contents take longer to pass through the gut, and leading to constipation.
Heavy periods:
- Hypothyroidism inhibits ovulation, leading to disordered menstrual cycles and heavy periods. It is also associated with raised prolactin levels which also inhibit ovulation.
Pregnancy loss:
- An underactive thyroid is a recognised cause of various complications of pregnancy – notable, anaemia, miscarriage, stillbirth, preeclampsia, and low birth weight. This is because if there is not enough thyroxine, the body’s metabolic processes cannot work properly.
A hoarse voice:
- When thyroxine levels are low, fluid can build up around the vocal cords, giving rise to a hoarse voice.
Raised cholesterol:
- When your thyroid is underactive it does not break down cholesterol in the gut so efficiently, and this can lead to a raised level of LDL ‘bad’ cholesterol. This is a risk factor for cardiovascular disease.
A swelling in the neck:
- People with iodine deficiency characteristically have a swelling in the neck called a goitre. This is because the thyroid gland is working overtime, trying to cope with too little iodine. A goitre can be associated with a cough, shortness of breath and/or a hoarse voice. There are other causes of goitres – for example – a goitre can also be present if the thyroid is overactive (hyperthyroidism).

Dietary intake of iodine

To ensure you are getting enough iodine in your diet, you need to make sure your diet is varied, balanced, and nutritionally complete. It’s important to regularly eat fish and seafood, and also dairy milk and milk products – or plant milk but fortified with iodine.

It is possible to buy iodised salt. Take care not to consume too much iodine as this can also be harmful to health. You only need additional iodine if you do not eat fish or drink milk, are vegan or vegetarian, or are advised to do so by your doctor.

Association of UK Dieticians – Iodine: Food Factsheet

When should you have a thyroid blood test?

If you have noted any symptoms on the above list, go and discuss this with your GP.

If you are pregnant and have any history of thyroid disease, your GP should check your thyroid hormone levels in the first 4-6 weeks of pregnancy, regularly throughout the pregnancy, and again a few weeks after delivery (British Thyroid Foundation BTF)